Electronic component devices of interest to the present invention include, for example, a BAW filter. The BAW filter includes a main substrate provided with an electronic circuit forming section and a first sealing frame surrounding the electronic circuit forming section on one main surface of the main substrate, and a cover substrate provided with a second sealing frame to be bonded to the first sealing frame on one main surface of the cover substrate. Then, the main substrate and the cover substrate are disposed so that the main surfaces of the two substrates face each other, and in this state, the first sealing frame and the second sealing frame are bonded to each other to realize a structure in which the above-mentioned electronic circuit forming section is hermetically sealed.
The following technologies have been proposed as a technology for bonding the first sealing frame and the second sealing frame to each other to seal an electronic component device as described above.
First, a sealing technology based on a Cu—Sn alloy has been proposed in Japanese Unexamined Patent Publication No. 2004-194290 (Patent Document 1) and Japanese Unexamined Patent Publication No. 2006-135264 (Patent Document 2). This sealing technology will be described with reference to FIG. 7.
In FIG. 7, a part of each of a main substrate 1 and a cover substrate 2, which are disposed so as to face each other, is shown. As shown in FIG. 7(1), a first sealing frame 3 is formed on an upper main surface of the main substrate 1, and on the other hand, a second sealing frame 4 is formed on a lower main surface of the cover substrate 2 before a bonding step is performed. The first and second sealing frames 3 and 4 are composed of, for example, copper (Cu). An oxidation resistant film 5 composed of Au, for example, is formed on the first sealing frame 3 as required as shown by the dotted line. The oxidation resistant film 5 is a film for preventing the oxidation of Cu constituting the first sealing frame 3, and does not contributes directly to bonding described later. On the other hand, a Sn layer 6 predominantly composed of Sn having a lower melting point than Cu is formed on the second sealing frame 4. The Sn layer 6 functions as a bonding material.
In order to attain a state in which the first sealing frame 3 is bonded to the second sealing frame 4, the first sealing frame 3 and the second sealing frame 4 are brought into a contact state, in which the two frames face each other with the Sn layer 6 interposed therebetween, by applying pressure, and the first sealing frame 3 and the second sealing frame 4 are heated while maintaining the contact state. Consequently, first, Au constituting the oxidation resistant film 5 is dissolved in the Sn layer 6, and then, Cu constituting the first and second sealing frames 3 and 4 diffuses into the Sn layer 6 to produce an intermetallic compound of Cu and Sn.
More specifically, when heating in pressurization as described above is continued, the Sn layer 6 disappears, and first, a Cu6Sn5 layer 7 predominantly composed of Cu6Sn5 having a melting point of 415° C. is formed as shown in FIG. 7(2), and a Cu3Sn layer 8 predominantly composed of Cu3Sn having a melting point of 640° C. begins to be formed between the Cu6Sn5 layer 7 and each of the first sealing frame 3 and the second sealing frame 4.
When the heating in pressurization is further continued, the Cu6Sn5 layer 7 disappears as shown in FIG. 7(3), and a bonding structure, in which a bonding section 9 bonding the first sealing frame 3 to the second sealing frame 4 is constituted by the Cu3Sn layer 8, is attained.
In the bonding structure as describe above, it is important that the Cu6Sn5 layer 7 disappears and the bonding section 9 is constituted by the Cu3Sn layer 8. The reason for this is that if the Cu6Sn5 layer 7 remains, the interdiffusion between Cu and Sn further proceeds so that the Cu6Sn5 layer 7 will change to the Cu3Sn layer 8 when the bonding section 9 is exposed to used reflow or high-temperature environment for a long time, and so-called Kirkendall voids may be generated due to difference in diffusion coefficients between Cu and Sn during the interdiffusion proceeds to cause defective sealing.
In order to attain a state in which the Cu6Sn5 layer 7 disappears and the bonding section 9 is constituted by the Cu3Sn layer 8, it is necessary to diffuse Cu adequately into Sn, but the alloy growth rate of Cu3Sn is extremely small as shown in FIG. 8. In addition, FIG. 8 shows the growth rates of alloys at 300° C. Therefore, in order to attain a state in which the bonding section 9 is constituted by the Cu3Sn layer 8, for example, the condition that a temperature of 300° C. is held for 60 minutes under a pressure of 8.2 Mpa is required. Therefore, this process leads to a problem that productivity is low and production cost is high. Further, the above-mentioned conditions may be extreme conditions of impairing the quality of the electronic circuit forming section included in the electronic component device.
Patent Document 1: Japanese Unexamined Patent Publication No. 2004-194290
Patent Document 2: Japanese Unexamined Patent Publication No. 2006-135264